It's well known that high blood pressure puts you at risk of a host of health issues--such as heart attack, heart failure, stroke and atherosclerosis leading to peripheral artery disease--but the results of a new study suggest that it might also increase the risk of Alzheimer’s disease.

The study, which was funded by the National Institutes of Health (NIH), revealed that high blood pressure can lead to brain lesions and protein tangles in the brain, the latter of which are a well-known marker of Alzheimer’s disease. The study was titled “Late-life blood pressure association with cerebrovascular and Alzheimer disease pathology” and appeared in the July 11 online issue of Neurology.

The first and higher number in a blood pressure reading is the systolic blood pressure, while the second, lower number is the diastolic blood pressure.

“Blood pressure changes with aging and disease, so we wanted to see what kind of impact it may have on the brain,” said study author Dr. Zoe Arvanitakis, director of the Rush Alzheimer’s Disease Center's Memory Clinic at Rush University Medical Center. “We researched whether blood pressure in later life was associated with signs of brain aging that include plaques and tangles linked to Alzheimer’s disease, and brain lesions called infarcts, areas of dead tissue caused by a blockage of the blood supply, which can increase with age, often go undetected and can lead to stroke.”

The study followed 1,288 older participants until they died, for an average of eight years of monitoring and an average age at death of 89 years. Each participant's blood pressure was recorded annually, and after their death, autopsies were performed on their brains. Of the participants, two-thirds had a history of high blood pressure, with 87 percent taking medication for the issue, and the average systolic and diastolic blood pressure was 134 mm Hg and 71 mm Hg, respectively.

What the research team discovered during the autopsies was that 48 percent of the study participants had one or more brain infarct lesions, and the risk of such lesions was higher in those with higher systolic blood pressure. Those whose systolic blood pressure fell within one standard deviation above the average—say, 147 mm Hg rather than 134 mm Hg—faced a 46-percent greater chance of having one or more brain lesions, particularly infarcts. As noted in an American Academy of Neurology press release, “[T]he effect of an increase by one standard deviation on the risk of having one or more brain infarcts was the equivalent of nine years of brain aging.”

Diastolic blood pressure also impacted the likelihood of brain lesions. Those whose diastolic blood pressure was higher than the average by one standard deviation—79 mm Hg rather than 71 mm Hg—were 28 percent more likely to have one or more brain lesions. And more tellingly, these risks did not change even when accounting for other factors such as medication.

In terms of more traditional hallmarks of Alzheimer’s disease, the researchers saw a link between higher systolic blood pressure and a greater number of protein tangles, but not necessarily amyloid plaques.

“Further studies will be needed to confirm and expand on our findings,” Arvanitakis noted, as there were limitations to the study. Among those are the fact that blood pressure was only tested once a year and that the researchers only had access to participants' blood pressure late in life, not during middle age.

This is not the first study by an NIH organization to explore the connection between blood pressure and dementia. In August 2017, the National Institute of Neurological Disorders and Stroke (NINDS), part of the NIH, shared the results of a study looking at how vascular risk factors such as high blood pressure (as well as diabetes and smoking) can increase middle-aged individuals' chances of facing dementia late in life.

The study looked at the data from 15,744 individuals who took part in the Atherosclerosis Risk In Communities (ARIC) study, which was funded by the National Heart, Lung, and Blood Institute. Participants 45 to 64 years of age were tested from 1987 to 1989 as an initial examination, and then followed for 25 years, during which they were tested four more times. The team, led by Dr. Rebecca Gottesman, professor of neurology at Johns Hopkins University, found that of the participants, 1,516 were diagnosed with dementia in the span of an average of 23 follow-up years. They also found that those with high blood pressure or diabetes were more likely to develop dementia, with diabetes found to be “almost as strong a predictor of dementia as the presence of the APOE4 gene,” which has long since been linked to Alzheimer’s.

In a separate study, Gottesman and her team examined brain scans of ARIC study participants who did not have dementia at the beginning of the study, and found that having one or more vascular risk factors in their middle years was associated with higher levels of beta amyloid. In those older than 65 years of age, however, vascular risk factors were not associated with higher beta amyloid levels.

This news could be important for even more people now, in light of the new guidelines for blood pressure released by the American Heart Association, the American College of Cardiology and other organizations in 2017. The previous guidelines set the bar for diagnosing hypertension, or high blood pressure, at 140/90 mm Hg for individuals under the age of 65 and 150/80 mm Hg for individuals aged 65 and up. Now the target number is 130/80 mm Hg and higher for adults of any age. The Systolic Blood Pressure Intervention Trial (SPRINT for short) was the cause for the updated guidelines. That trial looked at more than 9,000 adults ages 50 and up with systolic blood pressure of 130 mm Hg or higher and a minimum of one risk factor for heart disease, and found that aiming for a systolic blood pressure of 120 mm Hg or less dropped participants' chance of heart attacks/failure or stroke over the course of three years.